Archaeology and Sclerochronology of Marine Bivalves

Downloaded from orbit.dtu.dk on: Sep 27, 2021 Archaeology and sclerochronology of marine bivalves Butler, Paul G.; Freitas, Pedro Seabra; Burchell, Meghan; Chauvaud, Laurent Published in: Goods and Services of Marine Bivalves Link to article, DOI: 10.1007/978-3-319-96776-9_21 Publication date: 2018 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Butler, P. G., Freitas, P. S., Burchell, M., & Chauvaud, L. (2018). Archaeology and sclerochronology of marine bivalves. In A. C. Smaal, J. G. Ferreira, J. Grant, J. K. Petersen, & Ø. Strand (Eds.), Goods and Services of Marine Bivalves (pp. 413-444). Springer. https://doi.org/10.1007/978-3-319-96776-9_21 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Chapter 21 Archaeology and Sclerochronology of Marine Bivalves Paul G. Butler, Pedro S. Freitas, Meghan Burchell, and Laurent Chauvaud Abstract In a rapidly changing world, maintenance of the good health of the marine environment requires a detailed understanding of its mechanisms of change, and the ability to detect early signals of a shift away from the equilibrium state that we assume characterized it before there was any significant human impact. Given that instrumental measurements of the oceans go back no further than a few decades, the only way in which we can assess the long-term baseline variability that charac- terizes the pre-perturbation equilibrium state of the marine environment is by the use of proxy records contained in stratified or layered natural archives such as cor- als, fish otoliths and bivalve mollusc shells. In this chapter we will look at the ways in which the environmental signals recorded in the shells of bivalve molluscs can be used to shed light on marine variability both in the present and over past centuries and millennia, and specifically how they can be used to study marine climate, the marine environment and the economic and cultural history of the relationship between humans and the oceans. The chapter is divided into two parts: section one describes the morphological, geochemical and crystallographic techniques that are used to obtain information from the shells, while section two covers the use of bivalve shells in a wide range of P. G. Butler (*) College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Cornwall, UK e-mail: [email protected] P. S. Freitas Danish Shellfish Centre, Technical University of Denmark, Nykøbing M, Denmark e-mail: [email protected] M. Burchell Department of Archaeology, Faculty of Humanities & Social Sciences, Memorial University, St. John’s, NL, Canada e-mail: [email protected] L. Chauvaud IUEM-UBO, UMR CNRS 6539, Technopôle Brest-Iroise, Plouzané, France e-mail: [email protected] © The Author(s) 2019 413 A. C. Smaal et al. (eds.), Goods and Services of Marine Bivalves, https://doi.org/10.1007/978-3-319-96776-9_21 414 P. G. Butler et al. applications, including ecosystem services, environmental monitoring, archaeology, climate reconstruction, and climate modeling. Abstract in Chinese 摘要: 在瞬息万变的世界中,为了维护良好的海洋环境, 我们需要对其变化机制有一个详细的了解,以便能够及时获取和辨识由人为影响造成的海洋生态平衡状态改变的早期信号。近几十年来,,我们评估海洋环境平衡扰动的长期基线变化的唯一途径是记录在珊瑚礁,鱼耳石和贝类贝壳内不同年代的环境变化留下的信号。在本章中,我们将着眼于研究当下和过去的数百乃至数千年中双壳贝类壳中记录的环境信号,并基于这些信号来揭示长久以来海洋的变化情况,包括如何利用这些信息来进行海洋气候研究, 海洋环境研究以及人类与海洋相互作用在经济与文化方面情况。本章分为两部分:第一部分描述如何通过形态学,地球化学和晶体学技术从贝壳中获取信息;第二部分介绍了双壳类贝壳在生态系统服务,环境监测, 考古学,气候状态重构和气候模拟等研究中的应用。 Keywords Environmental monitoring · Mollusc · Archaeology · Marine climate · Ecosystems 关键词环境监测 · 软体动物 · 考古学 · 海洋气候 · 生态系统 21.1 Physical and Geochemical Proxies Everything that is known about past environmental and climatic conditions in the Earth’s history prior to the appearance of historical written records and the use of instrumental measurements is based on the identification and interpretation of proxies preserved in biological or geological structures. Proxies are measurable physical or chemical properties of biogenic or abiogenic structures (e.g. shells, coral skele- tons, trees, sediments, rocks) that can be interpreted as a signal of one or more environmental variables at the time during which the structures were formed. In addition, proxies enable monitoring of present day environmental conditions in locations where instrumental or historical observations are absent. The major challenge when using bivalve shell material as a proxy archive (this is common to all proxy archives) is to establish the causal link between the wider environment in which the animal was living and the form, or configuration, with which the proxy manifests itself in the carbonate shell material. This is necessary in order to isolate the influence of the large-scale environment on the proxy from the effects of biomineralization or micro-environments. Complicating factors include vital effects, fractionation, multiple drivers in the environment, diagenesis, temporal lags, determination of the season of growth, and variable growth rates (throughout ontogeny and within each year) (Schöne 2008). While these sources of uncertainty can never be fully eliminated, they can be partially compensated through greater replication of chronologies in space (as the real environmental signal emerges from the background noise) and through mathematical modelling (Mueller et al. 2015; 21 Archaeology and Sclerochronology of Marine Bivalves 415 Goodwin et al. 2009; De Ridder et al. 2004) or forward modeling of the processes of shell growth (Tolwinski-Ward et al. 2011). The main proxies used in bivalve sclerochronology are: variations in periodic shell growth (usually in the form of daily, tidally or annually deposited increments); stable oxygen, carbon and nitrogen isotopes and elemental composition of the shell; and changes in the shell crystal microstructure. 21.1.1 Shell Growth Shell growth reflects the complex interactions of biological clocks and physiologi- cal processes with recurrent environmental pacemakers such as light/dark cycles, tidal exposure and diurnal or seasonal temperature variations. Interruption or reduc- tion of shell growth results in the formation of distinct lines or bands (see Fig. 21.1), which delimit periodic growth increments at a range of temporal scales from sub- daily to annually. Fig. 21.1 Annually-resolved growth increments imaged in the umbone (hinge) region of a speci- men of Glycymeris glycymeris. Each increment (the wide lighter bands between the thin dark lines) consists of material laid down during the growth season (usually between 6 and 9 months). (Photo: Pedro Freitas) 416 P. G. Butler et al. While it is a challenging task to disentangle the signals of multiple environmental or climatic drivers in time-series of bivalve growth increments, growth increment series have been interpreted as a response to climate patterns in the Arctic (Ambrose et al. 2006) and north Atlantic (Reynolds et al. 2017, Swingedouw et al. 2015, Schöne et al. 2003,), west African monsoon activity (Azzoug et al. 2012), sea sur- face temperature (Brocas et al. 2013; Reynolds et al. 2013; Black et al. 2009; Butler et al. 2010) and palaeo-productivity (Wanamaker et al. 2009; Witbaard 1996). 21.1.2 Stable Isotopes The ability to use stable isotopes as geochemical proxies relies on the fractionation (i.e. the relative preference) between the lighter and heavier isotopes of an element during chemical reactions (e.g. carbonate precipitation or respiration) and the pres- ervation of the resultant stable isotope ratio in the shell material. Stable isotope ratios of oxygen and carbon are commonly used in bivalve shells, while the use of stable isotope ratios of other elements (e.g. magnesium, boron, nitrogen, sulphur or strontium) is less common (e.g. Levin et al. 2015; Liu et al. 2015; Carmichael et al. 2008; Holmden and Hudson 2003), as is the use of clumped isotopes (Eagle et al. 2013). 21.1.2.1 Stable Oxygen Isotopes 18 The stable oxygen isotope ratio (δ Oshell) of shell carbonate depends on both the ambient temperature and the isotopic composition of the water, the latter being influenced by precipitation-evaporation dynamics and water mass mixing, thus being correlated (in marine environments) with salinity (Carmichael et al. 2008; Epstein et al. 1953; Urey 1947). Empirical palaeotemperature equations have been 18 developed to reconstruct temperature from δ Oshell (e.g. Kim and O’Neil 1997; 18 Grossman and Ku 1986), although these assume that δ Owater is known or can be estimated. Bivalves usually precipitate their shell calcite and aragonite in or close to oxygen isotopic equilibrium (e.g. Wefer and Berger 1991) and palaeotemperature equations have been produced for several bivalve species, including Pecten maxi- mus (Chauvaud et al. 2005), Mytilus edulis (Wanamaker et al. 2007), Glycymeris glycymeris(Royer et al. 2013), Tridacna gigas (Aharon 1983)

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